# -*- coding: latin-1 -*-
# Copyright (c) 2007-2009 Jorge Ortiz Romo <jortizromo@gmail.com>
#                         Freymam Vallejo Cuero <freturn@gmail.com>
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation
# files (the "Software"), to deal in the Software without
# restriction, including without limitation the rights to use,
# copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the
# Software is furnished to do so, subject to the following
# conditions:

# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
# OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
# HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
# WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
# OTHER DEALINGS IN THE SOFTWARE.


'''
Created on Dec 7, 2009

@author: Freymam Vallejo
@author: Jorge Ortiz
'''

from __future__ import division


def digraph_density(digraph):
    """
    Proportion of arcs present in the digraph.

    @type graph: Digraph.
    @param graph: digraph.

    @rtype: number.
    @return: Takes values between 0 and 1.
    """

    #Gets amount of edges
    edges_len = digraph.edges().__len__()
    #Gets amount of nodes
    nodes_len = digraph.nodes().__len__()
    
    #Calculates the ecuation for density
    try: density = edges_len / (nodes_len * (nodes_len - 1))
    except ZeroDivisionError: return 0 

    #Return density
    return density
